Polymer foam particles and process for production thereof based on polybutylene terephthalate

ABSTRACT

The invention relates to polymer foam particles, both in expanded and partly expanded form, from a polymer matrix based on a blend comprising polybutylene terephthalate and polyethylene terephthalate, to a process for production thereof, and to the use of polyethylene terephthalate for broadening the processing window of polybutylene terephthalate-based polymer foam particles in processing to give mouldings.

This application claims the benefit of priority of European PatentApplication No. 21171405.0, filed on Apr. 30, 2021, the disclosure ofwhich is hereby incorporated by reference.

The invention relates to polymer foam particles, both in expanded andpartly expanded form, from a polymer matrix based on a blend comprisingpolybutylene terephthalate and polyethylene terephthalate, to a processfor production thereof, and to the use of polyethylene terephthalate forbroadening the processing window of polybutylene terephthalate-basedpolymer foam particles in processing to give mouldings.

BACKGROUND OF THE INVENTION

Thermoplastic-based polymer foam particles that are expandable or havebeen partly expanded by means of a blowing agent find use primarily forproduction of polymer mouldings. For this purpose, they aresuperficially welded to one another in a corresponding mould, especiallyunder the action of hot steam, to form a moulding. If a proportion ofthe blowing agent is still present in the polymer foam particles, theseare expanded/foamed in the mould, which can achieve a large-area weldbond of the polymer foam particles to one another, and by means of whicha low-density moulding is obtainable.

Alternatively, expandable or partly expanded polymer foam particles canbe heated under the action of electromagnetic radiation, especially inthe microwave/radiofrequency range or the like, in order likewise toweld them to one another in a mould. If the polymers used in each casedo not themselves have sufficient absorption capacity for the respectivefrequency range of the electromagnetic radiation, they can becoated/wetted with a medium that absorbs electromagnetic radiation, forexample in the microwave and/or radiofrequency spectrum, especiallywater.

Polymer mouldings produced in this way, on account of thecompressibility of the polymer foam formed from the expanded andmutually fused polymer foam particles, are notable for low density, andhigh heat, sound and impact absorption capacity. They are therefore usedprimarily for insulation materials, such as insulation panels forinsulation of buildings or other insulation components, for example forroller shutter boxes, window profiles, for heating construction, forinsulated vessels and the like, in automobile technology, for packagingmaterials, as core materials of sandwich-type mouldings, for examplesports articles, surfboards, boat bodies etc., or for furniturebuilding. Furthermore, fields of use for loose polymer foam particles,i.e. expanded polymer foam particles that have not been welded to oneanother to form a moulding, are, for example, as filler materials forpackaging purposes, for beanbags and the like, as insulation materialsfor blow-in insulation, or else as imitation snow, for example fordecorative purposes.

In practice, the production of expandable or partly expanded polymerfoam particles from thermoplastic polymers is accomplished primarilywithin an extrusion operation, followed by a pelletizing operation onthe polymer strand exiting from the die or a die assembly of anextruder. The thermoplastic base polymer is introduced in powder orpellet form into an extruder, and plastified and homogenized therein.Then a blowing agent—if one is not already present in the powder orpellets used—is introduced into the plastified material, preferablyunder pressure. On account of the pressure level in the extruder, whichmay be up to a few hundred bar, the blowing agent is in the liquidand/or supercritical phase even at the melting temperature of theplastified polymer, and is especially dissolved in the plastifiedmaterial. Immediately after exiting from the extruder die, as a resultof the abrupt drop in pressure, especially ambient pressure, there isexpansion and foaming of the polymer strand on account of rapidexpansion of the blowing agent into the gas phase. In the case of use ofa die plate as extruder outlet, multiple polymer strands are obtained,in which the blowing agent expands simultaneously. The comminution orpelletization of the polymer strand(s) is typically accomplished bymeans of a cutting device downstream of the extruder. This is preferablya cutter that rotates coaxially to the extruder nozzle. While it is alsoknown in the case of compact or unfoamed polymers to guide the polymerstrand(s) through a water bath, followed by pelletization aftersufficient cooling, expanded or foamed polymers are comminuted by meansof the cutting device, for example in a water-filled chamber, in orderto rapidly cool the polymer strand with added blowing agent and to“freeze” the fine-pore foam structure formed in the expansion of theblowing agent.

In order to ensure a very homogeneous, intimate weld bond of theexpandable polymer foam particles, or those that have already at leastpartly expanded in the pelletizing operation, in a polymer mouldingproduced therefrom, it is generally desirable for the polymer foamparticles to have a very substantially spherical but at least roundedoutline. On production of the polymer foam particles themselves, thisresults in the requirement to comminute or pelletize the foaming polymerstrand emerging from the extruder die very rapidly to give the polymerfoam particles, since a spherical shape of the particles is achievableespecially when the polymer strand is still in an at least semiplasticstate. In addition, however, the polymer emerging from the extruder dieshould also be cooled or “quenched” very rapidly for an essentiallyhomogeneous, fine-pore foam structure to form and for the bubbles formedfrom expanded blowing agent in the polymer matrix not to collapse.

It is also known that the expanding or foaming operation can beundertaken separately from the extruding operation, in that the polymerstrand exiting from the extruder die, in very substantially unfoamedform, is first pelletized and then foamed—for example with hot steam ina foaming unit, initiated by a suitable blowing agent present in thepolymer pellets.

While, on the one hand, primarily thermoplastic polymers originatingfrom fossil raw materials are used in practice for the production ofexpandable or partly expanded polymer foam particles, there is researchon the other hand into options for production of novel polymer foamparticles and the associated challenges on processing and mouldtechnology. Among the materials attracting increasing attention areengineering thermoplastics that can also be used as matrix material forfibre-polymer composites in applications at elevated temperatures. Thisenables combination of the excellent thermal and mechanical propertiesof engineering plastics with the low density of foams, and tailoring ofthe characteristics of material composites.

Extremely lightweight particle foam structures in the form of what arecalled sandwich concepts are likewise gaining increasing attention inresearch and development with regard to development of solutions tocounter rising costs in the case of mineral oil-based fuels, tosatisfaction of stricter legal provisions with regard to CO₂ emissionsof motor vehicles or to implementation of thermal insulation. Forexample, in the field of electromobility, polymer foam is becoming evermore important as a thermally insulating core material. Future materialsare likely to be multimaterial systems with foam cores made fromthermoplastic foam particles.

However, polyester-based foams to date have a comparatively small rangeof application compared to polystyrene or polyurethane foams on accountof processing-related challenges and typically high densities. Severalhurdles have to be overcome for the successful implementation of aparticle foam made from polybutylene terephthalate (PBT). Firstly, PBThas a low melt stability typical of polyesters, which is a barrier tohigh expansion during foaming. Secondly, the partial crystallinityresults in a comparatively narrow processing window in the adjustment ofthe melting temperature during the foaming process.

However, polybutylene terephthalate [CAS No. 24968-12-5] is of excellentsuitability for use in injection moulding at melt temperatures of 230 to270° C., and has favourable cooling and processing characteristics (J.Falbe, M. Reglitz, RÖMPP Lexikon Chemie [RÖMPP's Chemical Lexicon],volume 5: Pl-S, 10th edition, Thieme, 1998). The melting point of PBT isreported as 223° C.; its glass transition temperature is 47° C.; theglass transition of the amorphous phase is at 60° C. Polybutyleneterephthalate is valued especially owing to its high strength andstiffness, its very high dimensional stability compared topolyoxymethylene or polyamide, and its very good friction and wearproperties.

The narrow melting range of the PBT crystals, which considerablyrestricts the processing window of PBT in particle foaming inparticular, increases the demands on processing technology to a veryparticular degree. Experience has shown that the processing window ofPBT is 225+/−2° C.

The melt stability of polyesters such as PBT, which is additionally lowand therefore disadvantageous in foaming processes, was examined by T.Standau et. al., in Ind. Eng. Chem. Res. 2018, 57, 17170-17176. The mainproblems in the production of particle foams from PBT are consideredtherein to be

-   -   (i) the necessity of improving the rheological properties        (including the low melt stability),    -   (ii) fitting into the narrow processing window and    -   (iii) the fusion of the polymer foam particles.

Standau therefore uses the chain extender Joncryl® ADR 4468. This is astyrene-acrylate copolymer with epoxy functionality for improvement ofmelt viscosity; see also V. Frenz et. al., Multifunctional Polymers asChain Extenders and Compatibilizers for Polycondensates and Biopolymers,ANTEC 2008, 1682-1686.

A disadvantage of the prior art solution is the introduction ofstyrene-acrylate polymer and hence a different type of polymer into thePBT. In spite of this advance, there is still a great need forexpandable polyester pellets and polyester foams based on PBT that arenotable not only for a low density but also for ease of processabilityand high degrees of freedom in shaping, especially since they are usablein a very resource-conserving manner, since the density of the foam andhence the raw material requirement and the foam properties can beestablished in the prefoaming operation. Foam particles can be foamed togive blocks or complex particle foam structures or mouldings in onestep. If such particle foam structures are used in motor vehicleconstruction, however, these should be able to withstand thetemperatures during an electrochemical painting method (cathodicelectrocoating) in which the object to be painted is subjected to a bathof aqueous electrocoat under a DC voltage of 3000 volts and 220 to 290amperes, and then the resultant coating is baked in a cathodicelectrocoating drying oven at 200° C. for about 30 minutes.

It has now been found that, surprisingly, thermoplastic expandable orpartly expanded polymer foam particles based on a polymer matrix madefrom polybutylene terephthalate (PBT) can be produced by modifying thePBT with polyethylene terephthalate, which considerably broadens theprocessing window of the PBT in a foaming process without significantlyadversely affecting the other properties of the PBT.

SUBJECT-MATTER OF THE INVENTION

The present invention provides polymer foam particles comprising atleast one blowing agent selected from the group of air, nitrogen andcarbon dioxide, especially carbon dioxide, and 25 to 320 parts by massof polyethylene terephthalate per 100 parts by mass of polybutyleneterephthalate.

The invention also provides a process for producing polymer foamparticles, wherein powders or pellets of a polymer matrix

(a) are introduced into an extruder with exclusion of crosslinkingagents and/or chain-extending agents and plastified and homogenized,

(b) a blowing agent selected from the group of air, nitrogen and carbondioxide, especially carbon dioxide, is dispersed into the plastifiedpolymer matrix in an extruder,

(c) the plastified polymer matrix with the added blowing agent isdischarged from the extruder through an extruder die,

(d) the extruded polymer matrix strand with the added blowing agent ispelletized downstream of the extruder die to form expandable or at leastpartly expanded polymer foam particles, and

(e) the polymer foam particles are expanded, preferably thermallyexpanded, especially in a continuous infrared oven,

wherein the polymer matrix contains 25 to 320 parts by mass ofpolyethylene terephthalate per 100 parts by mass of polybutyleneterephthalate.

Preference is given to carrying out process steps (c) and (d) in or witha cooling fluid. The cooling fluid to be used in steps (c) and (d), in afurther embodiment, may be under elevated pressure. Elevated pressure inthe context of the present invention is preferably a pressure in therange from 1.5 to 30 bar.

By contrast with the prior art, in accordance with the invention, PETand PBT, in an ideal manner as thermoplastics of the same kind, areprocessed together with controlled establishment of the optimalprocessing window for foaming, it being possible to dispense with theadditional use of a polymer of a different kind.

The experiments in the context of the invention additionally show that,surprisingly, the use of PET in PBT reduces the growth rate of foamcells that arise at nucleation points. As a result, with use of PET tobe used in accordance with the invention, foam cells form at morenucleation points. This in turn leads, surprisingly, to PBT-basedpolymer foam particles with a more uniform cell structure composed ofsmall foam cells. This is because nucleation, i.e. the formation of acell nucleus, commences in the PBT polymer melts that are oversaturatedwith blowing gases. This oversaturation is typically achieved either bydecompression of a solution of a polymer and a physical blowing agent inthe equilibrium state, or by heating of a polymer melt with addeddecomposing chemical blowing agent. Mixed-in solid particles usually actas nucleation points in polymer melts. Once a foam cell has reached acritical size, the tendency of the blowing gas to diffuse in the foamcell causes it to grow until it is stabilized or bursts. The thin,significantly expanded cell walls in thermoplastic melts areintrinsically unstable unless they are stabilized. Foam cells maytypically be either physically or chemically stabilized. If physicalblowing agents are used and expansion is achieved by means ofdecompression, foam cells are physically stabilized. Foam cells arestabilized here on account of an abrupt rise in the modulus ofelasticity as a result of the biaxial extension of the foam cell walls.This effect is also referred to as strain-hardening. The rate of foamcell expansion also influences the strain-hardening effect. The phaseseparation of the blowing gas in the foam cell wall stabilizationadditionally plays a crucial role. The formation of the gas phase bringsabout a cooling effect through removal of heat from the polymer melt.The cooling effect increases the extensional viscosity of the melt. Thesuitability of a polyester type for physical stabilization is equivalentto suitability for achieving closed-cell structures and is referred toas “foamability of the polymer”.

In order to trigger the foaming of a blowing fluid-laden melt at themould exit, the sorption capacity of the polymer to be foamed must bereduced. According to Henry's law, this can in principle be achieved intwo ways: by an increase in temperature or a reduction in pressure.Since plastics are generally poor heat conductors and an increase intemperature would also lower the melt viscosity, oversaturation of themelt with blowing fluid is achieved in practice by a reduction inpressure. However, the experiments in the context of the presentinvention show that, surprisingly, the use of PET in PBT increases themelt viscosity of the PBT. The invention therefore also relates to theuse of PET for increasing the melt viscosity of PBT from 109 to 112 Pa·sup to >200 Pa·s (Pa·scal×second), preferably of PBT for production ofparticle foams. The melt viscosity of PBT is increased especiallypreferably when talc is used in addition to the PET.

The invention also provides a method of broadening the processing windowof PBT as matrix polymer in in-mould foaming by extending the meltingrange of PBT-based expandable or at least partly expanded polymer foamparticles from 225+/−2° C. to a range from 223 to 255° C., using 25 to320 parts by mass of polyethylene terephthalate per 100 parts by mass ofpolybutylene terephthalate.

The invention also preferably provides a method of broadening theprocessing window of PBT as matrix polymer in in-mould foaming byextending the melting range of PBT-based expandable or at least partlyexpanded polymer foam particles from 225+/−2° C. to a range from 223 to255° C., using 25 to 320 parts by mass of polyethylene terephthalate per100 parts by mass of polybutylene terephthalate and 0.1 to 20 parts bymass, preferably 0.1 to 5 parts by mass, of talc.

The invention also relates to the use of polyethylene terephthalate forbroadening the processing window of polybutylene terephthalate in theform of matrix polymer-containing expandable or at least partly expandedpolymer foam particles in in-mould foaming of polybutylene terephthalatefrom 225° C.+/−2° C. to the range from 223 to 255° C. and/or forincreasing the melt viscosity of polybutylene terephthalate to be usedas matrix polymer for expandable or at least partly expanded polymerfoam particles in in-mould foaming, in that 25 to 320 parts by mass ofpolyethylene terephthalate are used per 100 parts by mass ofpolybutylene terephthalate.

The invention preferably also relates to the use of polyethyleneterephthalate for broadening the processing window of polybutyleneterephthalate in the form of matrix polymer-containing expandable or atleast partly expanded polymer foam particles in in-mould foaming ofpolybutylene terephthalate from 225° C.+/−2° C. to the range from 223 to255° C. and/or for increasing the melt viscosity of polybutyleneterephthalate to be used as matrix polymer for expandable or at leastpartly expanded polymer foam particles in in-mould foaming, in that 25to 320 parts by mass of polyethylene terephthalate and 0.1 to 20 partsby mass, preferably 0.1 to 5 parts by mass, of talc are used per 100parts by mass of polybutylene terephthalate.

The PBT-based polymer foam particles according to the invention areexpandable or at least partly expanded polymer foam particles forproduction of particle foams or sandwich structures based thereon.

For the sake of clarity, it should be noted that the scope of thepresent invention encompasses all the definitions and parameters citedin general or in preferred ranges in any desired combinations. Thisapplies to the polymer foam particles, to the production processtherefor, and to the uses described in the context of the presentinvention. The standards cited in the context of this application relateto the current edition on the filing date of the present invention.

FURTHER PREFERRED EMBODIMENTS OF THE INVENTION

The present invention preferably provides polymer foam particles havinga density in the range from 50 to 700 kg/m³, comprising at least oneblowing agent selected from the group of air, nitrogen and carbondioxide, especially carbon dioxide, and 25 to 320 parts by mass ofpolyethylene terephthalate per 100 parts by mass of polybutyleneterephthalate.

The present invention more preferably provides polymer foam particleshaving a density in the range from 90 to 400 kg/m³, comprising at leastone blowing agent selected from the group of air, nitrogen and carbondioxide, especially carbon dioxide, and 25 to 320 parts by mass ofpolyethylene terephthalate per 100 parts by mass of polybutyleneterephthalate.

The present invention even more preferably provides polymer foamparticles having a density in the range from 50 to 700 kg/m³, comprisingat least one blowing agent selected from the group of air, nitrogen andcarbon dioxide, especially carbon dioxide, and 25 to 320 parts by massof polyethylene terephthalate and 0.1 to 20 parts by mass, preferably0.1 to 5 parts by mass, of talc per 100 parts by mass of polybutyleneterephthalate.

The present invention even more especially preferably provides polymerfoam particles having a density in the range from 90 to 400 kg/m³,comprising at least one blowing agent selected from the group of air,nitrogen and carbon dioxide, especially carbon dioxide, and 25 to 320parts by mass of polyethylene terephthalate and 0.1 to 20 parts by mass,preferably 0.1 to 5 parts by mass, of talc per 100 parts by mass ofpolybutylene terephthalate.

In a preferred embodiment, the present invention relates to a processfor producing polymer foam particles, preferably having a density in therange from 50 to 700 kg/m³, more preferably having a density in therange from 90 to 400 kg/m³, wherein powders or pellets of a polymermatrix

(a) are introduced into an extruder with exclusion of crosslinkingagents and/or chain-extending agents and plastified and homogenized,

(b) a gaseous blowing agent selected from the group of air, nitrogen andcarbon dioxide is dispersed into the plastified polymer matrix in anextruder,

(c) the plastified polymer matrix with the added blowing agent isdischarged from the extruder through an extruder die,

(d) the extruded polymer matrix strand with the added blowing agent ispelletized downstream of the extruder die to form expandable or at leastpartly expanded polymer foam particles, and

(e) the polymer foam particles are expanded, preferably thermallyexpanded, especially in a continuous infrared oven,

wherein the polymer matrix contains 25 to 320 parts by mass ofpolyethylene terephthalate and 0.1 to 20 parts by mass, preferably 0.1to 5 parts by mass, of talc per 100 parts by mass of polybutyleneterephthalate. Preference is given to carrying out steps (c) and (d) inor with a cooling fluid.

In an alternative or preferred embodiment, prior to process step (e),the pelletized polymer foam particles are contacted with blowing agentin an autoclave under suitable pressure over a suitable period of time.The appropriate conditions can be ascertained by a person skilled in theart by appropriate experimentation.

Preferably, in the process according to the invention, prior to processstep (e), the blowing agent used is carbon dioxide. The PBT/PET-basedpolymer foam particles according to the invention therefore containsolely carbon dioxide as blowing agent in a preferred embodiment.According to the invention, therefore, the PET to be used is used incombination with carbon dioxide as blowing agent, preferably in furthercombination with talc.

In a further preferred embodiment, in the polymer foam particles, butalso in the process according to the invention and in the use of the PETaccording to the invention, 0.1 to 20 parts by mass, more preferably 0.1to 5 parts by mass, of at least one additive other than talc per 100parts by mass of PBT is used in addition to talc.

Preferred additives other than talc are selected from the group of UVstabilizers, thermal stabilizers, lubricants and demoulding agents,fillers and reinforcers, nucleating agents other than talc, laserabsorbers, di- or polyfunctional branching or chain-extending additives,hydrolysis stabilizers, antistats, emulsifiers, plasticizers, processingauxiliaries, flow auxiliaries, elastomer modifiers and colourants. Theseadditives may be used alone or in admixture/in the form ofmasterbatches.

Lubricants and mould release agents other than talc that are preferredas additive are selected from the group of the long-chain fatty acids,the salts of long-chain fatty acids, the ester derivatives of long-chainfatty acids, and also montan waxes. Preferred long-chain fatty acids arestearic acid or behenic acid. Preferred salts of the long-chain fattyacids are calcium or zinc stearate. Preferred ester derivatives oflong-chain fatty acids are those based on pentaerythritol, moreparticularly C₁₆-C₁₈ fatty acid esters of pentaerythritol [CAS No.68604-44-4] or [CAS No. 85116-93-4]. Montan waxes in the context of thepresent invention are mixtures of straight-chain saturated carboxylicacids having chain lengths of from 28 to 32 carbon atoms. Particularpreference is given in accordance with the invention to using lubricantsand/or mould release agents from the group of esters of saturated orunsaturated aliphatic carboxylic acids comprising 8 to 40 carbon atomswith aliphatic saturated alcohols comprising 2 to 40 carbon atoms andmetal salts of saturated or unsaturated aliphatic carboxylic acidscomprising 8 to 40 carbon atoms, with particular preference forpentaerythritol tetrastearate [CAS No. 115-83-3], calcium stearate [CASNo. 1592-23-0] and/or ethylene glycol dimontanate, in particularLicowax® E [CAS No. 74388-22-0] from Clariant, Muttenz, Basel, and veryespecially particular preference for pentaerythritol tetrastearate, forexample obtainable as Loxiol® P861 from Emery Oleochemicals GmbH,Dusseldorf, Germany.

Colourants other than talc that are preferred as additive are organicpigments, preferably phthalocyanines, quinacridones, perylenes and dyes,preferably nigrosin or anthraquinones, and also inorganic pigments,especially titanium dioxide and/or barium sulfate, ultramarine blue,iron oxide, zinc sulfide or carbon black.

Plasticizers other than talc that are preferred as additive are dioctylphthalate, dibenzyl phthalate, butyl benzyl phthalate, hydrocarbon oilsor N-(n-butyl)benzenesulfonamide.

Nucleating agents other than talc to be used with preference as additiveare sodium or potassium salts of acetate, salicylate, stearate,saccharinate, and partly hydrolysed montan waxes and ionomers.

Heat stabilizers other than talc that are preferred as additive areselected from the group of sterically hindered phenols and aliphaticallyor aromatically substituted phosphites, and variously substitutedrepresentatives of these groups. Among the sterically hindered phenols,preference is given to those having at least one3-tert-butyl-4-hydroxy-5-methylphenyl unit and/or at least one3,5-di(tert-butyl-4-hydroxyphenyl) unit, particular preference beinggiven to hexane-1,6-diolbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] [CAS No.35074-77-2] (Irganox® 259 from BASF SE, Ludwigshafen, Germany),pentaerythritoltetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] [CAS No.6683-19-8] (Irganox® 1010 from BASF SE) and3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane[CAS No. 90498-90-1] (ADK Stab® AO 80). ADK Stab® AO 80 is commerciallyavailable from Adeka-Palmerole SAS, Mulhouse, France.

Among the aliphatically or aromatically substituted phosphonites,preference is given to usingtetrakis(2,4-di-tert-butylphenyl)-4,4-biphenyldiphosphonite [CAS No.119345-01-6], available for example from Clariant International Ltd,Muttenz, Switzerland, under the Hostanox® P-EPQ name,bis(2,4-dicumylphenyl)pentaerythritoldiphosphite [CAS No. 154862-43-8],available for example from Dover Chemical Corp., Dover, USA, under theDoverphos® S9228 trade name, and/ortetrakis(2,4-di-tert-butylphenyl)-1,1-biphenyl-4,4′-diylbisphosphonite[CAS No. 38613-77-3].

Elastomer modifiers other than talc that are preferred as additive areone or more graft polymers of at least one vinyl monomer D.1 and one ormore graft substrates D.2, having glass transition temperatures <10° C.,preferably <0° C., more preferably <−20° C., with use of preferably 5%to 95% by weight, more preferably amounts of 30% to 90% by weight, ofD.1 and 95% to 5% by weight, more preferably 70% to 10% by weight, ofD.2, where the percentages by weight relate to 100 per cent by weight ofelastomer modifier. Preferred embodiments of elastomer modifiers to beused in accordance with the invention are detailed in EP 3 239 228 A1,the contents of which are fully encompassed by the present invention.

Fillers or reinforcers other than talc that are to be used withpreference as additive are at least one from the group of mica,silicate, quartz, ground quartz, titanium dioxide, amorphous silicas,barium sulfate, glass beads, ground glass and/or fibrous fillers andreinforcers based on glass fibres or carbon fibres.

Particular preference is given to using glass beads or ground glass,very particular preference to using glass beads, as filler orreinforcer. When glass beads are used, figures for particle sizedistribution or particle sizes relate to what are called surfacearea-based particle sizes, each prior to incorporation into thethermoplastic moulding compound. The diameters of the areas of therespective glass particles are expressed here in relation to the surfaceareas of imaginary spherical particles (spheres). This is accomplishedwith a particle size analyser that works by the principle of laserdimming from Ankersmid (Eye Tech® including the EyeTech® software andACM-104 measurement cell, Ankersmid Lab, Oosterhout, the Netherlands).

The fillers and/or reinforcers other than talc that are to be used asadditive may, as a result of the processing to give the mouldingcompound or to give a particle foam structure according to theinvention, have a smaller d97 or d50 value therein than the fillers orreinforcers originally used. With regard to the d50 and d97 values inthis application, the determination thereof and the meaning thereof,reference is made to Chemie Ingenieur Technik (72) p. 273-276, 3/2000,Wiley-VCH Verlags GmbH, Weinheim, 2000, according to which the d50 valueis that particle size below which 50% of the amount of particles lie(median value) and the d97 value is that particle size below which 97%of the amount of particles lie.

The fillers and reinforcers other than talc that are to be used asadditive may be used individually or as a mixture of two or moredifferent fillers and/or reinforcers. In a preferred embodiment, thefiller and/or reinforcer for use as additive may have beensurface-modified, more preferably with an adhesion promoter/adhesionpromoter system, especially preferably an epoxide- or silane-basedadhesion promoter/adhesion promoter system. However, pretreatment is notabsolutely necessary. Preferred embodiments of adhesion promoters to beused in accordance with the invention are likewise given in EP 3 239 228A1.

Particular preference is given to using, in addition to talc asadditive, tetrakis(2,4-di-tert-butylphenyl) 4,4-biphenyldiphosphonite(Hostanox® P-EPQ).

The present invention preferably provides a process for producingpolymer foam particles, preferably having a density in the range from 50to 700 kg/m³, wherein powders or pellets of a polymer matrix

(a) are introduced into an extruder with exclusion of crosslinkingagents and/or chain-extending agents and plastified and homogenized,

(b) a blowing agent selected from the group of air, nitrogen and carbondioxide is dispersed into the plastified polymer matrix in an extruder,

(c) the plastified polymer matrix with the added blowing agent isdischarged from the extruder through an extruder die,

(d) the extruded polymer matrix strand with the added blowing agent ispelletized downstream of the extruder die to form expandable or at leastpartly expanded polymer foam particles, and

(e) the polymer foam particles are expanded, preferably thermallyexpanded, especially in a continuous infrared oven,

wherein the polymer matrix contains 25 to 320 parts by mass ofpolyethylene terephthalate, 0.1 to 20 parts by mass, preferably 0.1 to 5parts by mass, of talc and 0.1 to 20 parts by mass, preferably 0.1 to 5parts by mass, of tetrakis(2,4-di-tert-butylphenyl)4,4-biphenyldiphosphonite per 100 parts by mass of polybutyleneterephthalate. Preference is given to carrying out steps (c) and (d) inor with a cooling fluid.

The invention preferably also provides a method of broadening theprocessing window of PBT as matrix polymer in the production ofthermoplastic, expandable or at least partly expanded polymer foamparticles, by extending the melting range of pure PBT from 225+/−2° C.to the range from 223 to 255° C., wherein 25 to 320 parts by mass ofpolyethylene terephthalate, 0.1 to 20 parts by mass, preferably 0.1 to 5parts by mass, of talc and 0.1 to 20 parts by mass, preferably 0.1 to 5parts by mass, of tetrakis(2,4-di-tert-butylphenyl)4,4-biphenyldiphosphonite are used per 100 parts by mass of polybutyleneterephthalate.

Finally, the present invention preferably relates to the use ofpolyethylene terephthalate for broadening the processing window ofpolybutylene terephthalate in the form of matrix polymer-containingexpandable or at least partly expanded polymer foam particles inin-mould foaming of polybutylene terephthalate from 225° C.+/−2° C. tothe range from 223 to 255° C. and/or for increasing the melt viscosityof polybutylene terephthalate to be used as matrix polymer forexpandable or at least partly expanded polymer foam particles inin-mould foaming, in that 25 to 320 parts by mass of polyethyleneterephthalate and 0.1 to 20 parts by mass, preferably 0.1 to 5 parts bymass, of talc and 0.1 to 20 parts by mass, preferably 0.1 to 5 parts bymass, of tetrakis(2,4-di-tert-butylphenyl) 4,4-biphenyldiphosphonite areused per 100 parts by mass of polybutylene terephthalate.

Polybutylene Terephthalate (PBT)

The polybutylene terephthalate (PBT) to be used in accordance with theinvention is prepared from terephthalic acid or the reactive derivativesthereof and butanediol by known methods (Kunststoff-Handbuch [PlasticsHandbook], vol. VIII, p. 695 ff., Karl Hanser Verlag, Munich 1973). ThePBT to be used preferably contains at least 80 mol %, preferably atleast 90 mol %, of terephthalic acid radicals based on the dicarboxylicacid.

In one embodiment, the PBT to be used in accordance with the inventionas base polymer may contain not only terephthalic acid radicals but alsoup to 20 mol % of radicals of other aromatic dicarboxylic acids having 8to 14 carbon atoms or radicals of aliphatic dicarboxylic acids having 4to 12 carbon atoms, especially radicals of phthalic acid, isophthalicacid, naphthalene-2,6-dicarboxylic acid, 4,4′-diphenyldicarboxylic acid,succinic acid, adipic acid, sebacic acid, azelaic acid,cyclohexanediacetic acid, cyclohexanedicarboxylic acid orfuran-2,5-dicarboxylic acid.

In one embodiment, the PBT to be used in accordance with the inventionas base polymer may contain not only butanediol but also up to 20 mol %of other aliphatic diols having 3 to 12 carbon atoms or up to 20 mol %of cycloaliphatic diols having 6 to 21 carbon atoms, preferably radicalsof propane-1,3-diol, 2-ethylpropane-1,3-diol, neopentyl glycol,pentane-1,5-diol, hexane-1,6-diol, 1,4-cyclohexanedimethanol,3-methylpentane-2,4-diol, 2-methylpentane-2,4-diol,2,2,4-trimethylpentane-1,3-diol, 2,2,4-trimethylpentane-1,5-diol,2-ethylhexane-1,3-diol, 2,2-diethylpropane-1,3-diol, hexane-2,5-diol,1,4-di(β-hydroxyethoxy)benzene, 2,2-bi s(4-hydroxycyclohexyl)propane,2,4-dihydroxy-1,1,3,3-tetramethylcyclobutane,2,2-bis(3-β-hydroxyethoxyphenyl)propane and2,2-bis(4-hydroxypropoxyphenyl)propane.

PBT to be used with preference as base polymer has an intrinsicviscosity to be determined to EN-ISO 1628/5 in the range from 30 to 150cm³/g, more preferably in the range from 40 to 130 cm³/g, mostpreferably in the range from 50 to 100 cm³/g, in each case measured inan Ubbelohde viscometer in phenol/o-dichlorobenzene (1:1 part by weight)at 25° C. Intrinsic viscosity iV, also referred to as Staudinger Indexor limiting viscosity, is proportional, according to the Mark-Houwinkequation, to the average molecular mass, and is the extrapolation of theviscosity number VN for the case of vanishing polymer concentrations. Itcan be estimated from series of measurements or through the use ofsuitable approximation methods (e.g. Billmeyer). VN [ml/g] is obtainedfrom the measurement of the solution viscosity in a capillaryviscometer, for example an Ubbelohde viscometer. Solution viscosity is ameasure of the average molecular weight of a plastic. The determinationis effected on dissolved polymer using various solvents, preferablyformic acid, m-cresol, tetrachloroethane, phenol, 1,2-dichlorobenzene,etc., and concentrations. The viscosity number VN makes it possible tomonitor the processing and performance characteristics of plastics. Athermal load on the polymer, ageing processes or exposure to chemicals,weathering and light can be investigated by means of comparativemeasurements. In this regard, see also:de.wikipedia.org/wiki/Viskosimetrie andde.wikipedia.org/wiki/Mark-Houwink-Gleichung.

PBT preferred for use in accordance with the invention as base polymeris available from Lanxess Deutschland GmbH, Cologne under the namePocan® B 1300.

Polyethylene Terephthalate (PET)

Polyethylene terephthalate [CAS No. 25038-59-9] is a thermoplasticprepared by polycondensation from the family of the polyesters. PET hasvarious fields of use, and its uses include production of plasticbottles, films and textile fibres. Its density is 1.38 g/cm³; itsmelting point is 260° C. PET is virtually water-soluble and has a glasstransition temperature of 70° C. For further technical data see:de.wikipedia.org/wiki/Polyethylenterephthalat.

PET for use with preference in accordance with the invention has anintrinsic viscosity according to EN-ISO 1628/5 in the range from 30 to150 cm³/g, more preferably in the range from 40 to 130 cm³/g, mostpreferably in the range from 50 to 100 cm³/g, in each case measured inphenol/o-dichlorobenzene (1:1 parts by weight) at 25° C. in an Ubbelohdeviscometer. Intrinsic viscosity iV, also referred to as Staudinger Indexor limiting viscosity, is proportional, according to the Mark-Houwinkequation, to the average molecular mass, and is the extrapolation of theviscosity number VN for the case of vanishing polymer concentrations. Itcan be estimated from series of measurements or through the use ofsuitable approximation methods (e.g. Billmeyer). VN [ml/g] is obtainedfrom the measurement of the solution viscosity in a capillaryviscometer, for example an Ubbelohde viscometer. Solution viscosity is ameasure of the average molecular weight of a plastic. The determinationis effected on dissolved polymer, with various solvents (formic acid,m-cresol, tetrachloroethane, phenol, 1,2-dichlorobenzene, etc.) andconcentrations being used. The viscosity number VN makes it possible tomonitor the processing and performance characteristics of plastics. Athermal load on the polymer, ageing processes or exposure to chemicals,weathering and light can be investigated by means of comparativemeasurements. In this connection see also:de.wikipedia.org/wiki/Viskosimetrie andde.wikipedia.org/wiki/Mark-Houwink-Gleichung.

PET for use in accordance with the invention may be sourced as LighterC88 from Equipolymers s.r.l., Amsterdam, the Netherlands.

Process for Production of Polymer Foam Particles

It is found to be advantageous that the process according to theinvention can be conducted with exclusion of any crosslinking agentsand/or chain extenders such as Joncryl® ADR 4468, including those basedon epoxides, such that not only is the use of such substances that areharmful to the environment and health made dispensable, but thePBT-based polymer foam particles thus produced especially also have apolymer matrix formed from polyalkylene terephthalates of the same kind.

The prefoaming may preferably be effected in an autoclave process or bymeans of extrusion of a gas-laden melt.

In an alternative or else preferred embodiment, prior to process step(e), the pellets of expanded polymer foam particles are contacted withblowing agent in an autoclave under a pressure of 5 to 60 bar over aperiod of 2 to 60 h.

The PBT is preferably used in the form of a PET-blended masterbatch fromstep (a) in the extruder, and plastified and homogenized collectivelywith exclusion of crosslinking agents and/or chain extenders, withaddition of at least one blowing agent in process step (b) and withdispersion into the plastified polymer matrix of the PBT with the PETused as blend partner in the extruder. Then the polymer matrix composedof the blend with added blowing agent from process step (c) isdischarged from the extruder through at least one extruder die, and thenthe extruded polymer strand with the at least one blowing agent added ispelletized in process step (d) downstream of the extruder die to formthe polymer foam particles. Preference is given to carrying out processsteps (c) and (d) in or with a cooling fluid. In a preferred embodiment,the cooling fluid used is under an elevated pressure relative to ambientpressure.

In process step (e), the pellets, optionally with added blowing agent,are expanded, preferably thermally expanded, especially expanded in acontinuous infrared oven.

The at least one blowing agent, especially carbon dioxide, mayappropriately be added in a proportion of about 1% by mass to about 20%by mass, especially of about 2% by mass to about 15% by mass, preferablyof about 3% by mass to about 10% by mass, based on the mass of thepolymer matrix.

Preferably in accordance with the invention, talc is added to thePBT-based and PET-blended polymer matrix. Talc (magnesium silicatehydrate), as a fine particulate nucleating agent, ensures good bubbleformation in the expansion or foaming and also high crystallinity of thePET-blended PBT polymer matrix, and also high heat distortion resistancein a later application. Particular preference is given to using talc[CAS No.14807-96-6] in the form of microcrystalline talc. Talc is asheet silicate having the chemical composition Mg₃[Si₄O₁₀(OH)₂], which,depending on the modification, crystallizes as talc-1A in the tricliniccrystal system or as talc-2M in the monoclinic crystal system(de.wikipedia.org/wiki/Talkum). The talc to be used is commerciallyavailable, for example, under the name Mistron® R10 from Imerys TalcGroup, Toulouse, France (Rio Tinto Group).

While the cooling fluid used with preference in process steps (c) and(d) of the process according to the invention may in principle also be agas or gas mixture, it may be the case in an advantageous configurationthat the cooling fluid used is a liquid, especially an aqueous medium,for example water, which, on account of a comparatively high heatcapacity, is capable of ensuring a high cooling rate of the expandablepolymer foam particles produced in process step (d).

According to the desired bulk density of the expandable polymer foamparticles based on polybutylene terephthalate that are produced inprocess step (d), it may be the case that the cooling fluid is keptunder a pressure of

-   -   at least about 1.5 bar, especially at least about 2 bar,        preferably of at least about 5 bar; and/or    -   at most about 30 bar, especially at most about 25 bar,        preferably of at most about 20 bar.

A comparatively high pressure of the cooling fluid of at least about 5bar is capable of counteracting expansion or foaming of the polymer foamparticles on pelletization thereof in process step (d). Because thecooling fluid cools down the blowing agent-containing polymer foamparticles relatively quickly below their glass transition temperaturebased on the blend of PBT/PET, degassing is prevented and highly blowingagent-laden expandable polymer foam particles are produced. These have arelatively high bulk density and can be foamed solely by a mere thermaltreatment to give expanded polymer foam particles having very low bulkdensities and consequently very high pore volume. If the pressure of thecooling fluid, by contrast, is adjusted to a value of up to about 5 bar,the pelletizing in process step (d) may already induce at least partialexpansion or foaming of the polymer foam particles, so as to result inlower bulk densities of the partly foamed but nevertheless stillfurther-expandable polymer foam particles obtained against a higherpressure of the cooling fluid. The latter may preferably be an optionwhen the at least partly foamed polymer foam particles are not to bestored intermediately or transported onward over a prolonged period oftime but processed directly or promptly.

For the purposes mentioned, the cooling fluid may preferably be kept ata temperature of

-   -   at least about 0° C., especially at least about 5° C.,        preferably at least about 10° C.; and/or    -   at most about 90° C., especially at most about 70° C.,        preferably at most about 50° C.

The contacting of the pellets prior to process step (e) with at leastone blowing agent for production of expanded PBT-based polymer foamparticles, which is employed in an alternative or preferred embodimentof this invention, is effected in an autoclave under pressure.Preference is given here to employing pressures in the range from 5 to60 bar. Preference is given to contacting over a period of 2 to 60 h,which depends on the concentration of the blowing agent in the pelletsand the temperature in the autoclave that are desired in each caseaccording to the batch. Preference is given to employing at least oneblowing agent from the group of air, nitrogen and carbon dioxide, morepreferably carbon dioxide.

Once the pellets have absorbed sufficient blowing agent, especiallycarbon dioxide, they are removed from the autoclave and expanded,preferably thermally expanded, in process step (e). Especiallypreferably, the expansion is effected in a continuous infrared oven.During the expansion, the pellets that have been contacted with blowingagent, by absorbing radiation over a short period of time, take on thetemperature at which the blowing agent, especially carbon dioxide,causes the softened PBT and PET-modified polymer matrix to rise like ayeast dough. What takes a few minutes in the prior art, especially whensteam is used, and often requires subsequent conditioning proceeds in anentirely dry manner within a few seconds in accordance with theinvention. The speed of progression through the expansion process,especially in the continuous infrared oven, and the energy to beintroduced, especially the infrared source power in the continuousinfrared oven, must be adjusted in accordance with the PET-blended PBTpellets and the use amount thereof. During the expansion operation,especially during the passage through the continuous infrared oven, thePBT pellets that have been blended with PET in accordance with theinvention are heated to close to their softening temperature, whichallows the blowing agent incorporated to expand locally at nucleationpoints and to locally form cells that together produce a foam structure.The cell growth is determined by the pressure differential between theinterior of a cell and the medium surrounding the cell, by the diffusionof the blowing gas into existing cells, by the cooling effect resultingfrom the phase transformation of the blowing agent, and by theviscoelastic properties of the PET-blended or -modified PBT depending onthe melt temperature.

The cell growth process is described in principle in the thesis by Dipl.Ing. A. Braun “Verfahrensentwicklung von physikalisch geschäumtenPolypropylenplatten für den Einsatz als Kernmaterial vonSandwichverbunden” [Process Evolution of Physically Foamed PolypropyleneSheets for Use as Core Material of Sandwich Composites],Montanuniversität Leoben, January 2011 in chapter 2.5.6. Accordingly,cell growth in a polymeric foam is determined crucially by the exchangeof gas between melt and cell, and by the viscoelastic properties of thepolymer. While gas exchange is attributable to the above-addressedsorption and diffusion processes, viscoelastic properties are influencedmainly by the choice of polymer and the temperature control in theprocess. The polymer melt is subjected to biaxial extensional stress inthe cell walls. When the melt strength of the polymer melt is too low,the cell walls can break open, hence resulting in combination ofadjacent cells.

What is advantageous in accordance with the invention for cell growthand hence uniform foaming is a relatively high melt viscosity of the PBTachieved in the low shear viscosity range by virtue of the PET used. Thehigher melt viscosity of the PBT achieved by means of PET reduces thecoalescence of individual cells to form larger cells. As a result, theindividual cells remain relatively small and the structure of a foambead is homogeneous.

The degree of foaming depends on the amount of blowing agent/gasincorporated in the foam beads, and on the time taken to pass throughthe expansion process in process step (e), especially on the time takento pass through the continuous infrared oven and the source outputthereof. After passing through the expansion operation, especially afterpassing through the continuous infrared oven, the pellets may beprocessed further as polymer foam particles in the in-mould foamingprocess in the present case.

It is thus possible to set the desired bulk density of the polymer foamparticles to the desired value in a simple manner within relativelybroad intervals of preferably greater than 400 g/l to less than 100 g/l,by varying the duration of heat treatment and/or the proportion ofblowing agent to be used in accordance with the invention. The heattreatment for prefoaming of the polymer foam particles based on PBT canbe effected in virtually any desired manner. The heat treatment forprefoaming is preferably effected by means of correspondinglytemperature-controlled water vapour, air, water or other heat transferfluids, by exposure of the polymer foam particles to electromagneticradiation, preferably in the infrared region by means of a heat source,or with microwave or radiofrequency radiation or the like.

It is of course possible here in principle, at the above-described stageof prefoaming of the expandable polymer foam particles based on PBT thatare obtained in process step (d)—whether they are still essentiallycompact or whether they have already been at least partly expanded orfoamed, according to the cooling fluid pressure set—at elevatedtemperature to establish an elevated pressure relative to ambientpressure or else reduced pressure. However, the polymer foam particlesobtained in process step (d), for the reasons given, can be prefoamed ina simple and inexpensive manner, especially essentially at ambientpressure, in order to achieve the above-described very low bulkdensities or very high pore volumes.

In the context of the present invention, preference is given tocontacting PBT-based pellets containing PET and talc and optionally atleast one additive other than talc, especially Hostanox® P-EPQ, having adiameter in the range from 0.1 to 5 mm and a length in the range from0.1 to 10 mm, with blowing agent, especially CO₂, in an autoclave at apressure in the range from 5 to 100 bar over a period in the range from1 to 250 h. The pellets to be used preferably have a diameter in thediameter range from 0.5 to 2 mm. The pellets to be used preferably havea length in the range from 0.5 to 3 mm. The autoclave is preferablyoperated at a pressure in the range from 10 to 70 bar. Contacting withCO₂ is preferably effected over a period in the range from 5 to 50 h.

Subsequently, it has been found to be useful to guide the pellets thathave been contacted in accordance with the invention with blowing agent,especially CO₂, through a continuous infrared oven (single-lane SLcontinuous infrared oven from Fox Velution GmbH) with a source power inthe region of 90% (here: about 20 kW) at a temperature measured at thecontinuous infrared oven exit in the range from 220 to 255° C. (in thecontext of the present invention, reference band temperatures weremeasured optically because temperatures of 50° C. to 950° C. exist atdifferent positions in the oven itself) with a progression speed in therange from 300 to 1400 mm/s, preferably with a progression speed in therange from 500 to 800 mm/s. Finally, the particles are stabilized atroom temperature for 24 hours.

While the expandable and/or at least partly expanded polymer foamparticles based on PET-blended PBT produced by means of the process ofthe invention, as already described, can have variable bulk densitieswithin wide limits, it may be the case in an advantageous configurationthat they

-   -   have a proportion of PBT in the polymer matrix of at least 49%        by mass, especially of at least 60% by mass, preferably of at        least 75% by mass,    -   in the compacted state from process step (d) (i.e. before any        prefoaming) have a bulk density of at least 800 g/l,—after        foaming at a temperature in the range from 220° C. to 260° C.        over a period of 100 s at ambient pressure have a bulk density        of at most about 700 g/l, preferably of at most 400 g/l, more        preferably of at most 200 g/l, especially of at most 50 g/l.

Process for Production of Particle Foam Mouldings

The production of particle foam mouldings from polymer foam particles inmoulding machines is known to the person skilled in the art and,according to Kunststoffe 12/2010, Carl Hanser Verlag, Munich, pages134-137, comprises basically the following five stages:

-   -   closing the mould;    -   filling the mould cavity with simultaneous compression of the        polymer foam particles using compressed air;    -   softening, expanding and sintering the polymer foam particles        using steam;    -   cooling and stabilizing by means of cooling water, optionally by        vacuum assistance;    -   demoulding and optionally, for reasons of trueness to scale,        drying in temperature-controlled ovens.

Kunststoffe 12/2010 on page 135 describes a moulding machine forproduction of particle foam mouldings in FIG. 2, and shows a schematicof the particle foam process in FIG. 3. The polymer foam particles aresucked from a reservoir silo into a pressure filling system andcompressed. The precompressed polymer foam particles are filled into amould cavity through injectors by means of compressed air. Thecompression of the polymer foam particles influences the later mouldingdensity. Typically, there are nozzles in the mould cavity that havediameters in the region of tenths of millimetres, the function of whichis to assure devolatilization during the filling and introduction of theprocess steam. The process steam used here softens the polymer foamparticles to such an extent that sintering to give the moulding can takeplace. A cooling system in the mould accelerates the stabilization ofthe particle foam moulding and hence ensures relatively rapiddemouldability after a total cycle time of about 60 to 180 s accordingto the component geometry.

Until a few years ago, this steam-based processing of particle foam rawmaterial such as EPP (expanded polypropylene) and EPS (expandedpolystyrene) on moulding machines with process steam pressures of up to5 bar and hence maximum temperatures of up to max. 160° C., as describedin Kunststoffe 12/2010, pages 134-137, was state of the art. Therequired processing temperature is controlled here via the vapourpressure. The processing of engineering thermoplastics having acomparatively high melting or glass transition temperature, for instanceE-PBT and E-PET, generally also requires higher processing temperaturesthat cannot be established with standard processing equipment.

Cathodic electrocoating, which is customary nowadays in chassismanufacture, with high baking temperatures in the range from 200 to 230°C., for thermoplastic-containing motor vehicle components, requires amuch higher thermal stability of the thermoplastic to be used. For suchan application according to D. Schulz, VDWF im Dialog 4/2016, pages 3-7a corresponding particle foam based on expanded polybutyleneterephthalate (E-PBT) is suitable. Components made of E-PBT have ahigher thermal use limit by around 100° C., compared to EPP of the samedensity. Heat distortion resistance studies show that the specimensproduced from this material are still absolutely dimensionally stableand shape-stable even at 200° C. with exposure for more than 30 minutes.On account of the higher thermal stability, the processing of E-PBT alsorequires higher steam pressures of more than 10 bar. This in turn placeshigher demands on tools, machines and safety technology.

Particle foams based on PBT have higher densities than those based onEPP and EPS. This has to date considerably restricted their lightweightconstruction potential. This challenge can now be avoided firstlythrough the use of PET for broadening the processing window, and byloading the generally already prefoamed PBT-based polymer foam particlesunder elevated pressure with gas, preferably nitrogen, carbon dioxide orair, especially carbon dioxide, and foaming them further in subsequentsteps in order to reduce their density.

Process plants newly developed for the production of particle foams,also referred to as pressure and temperature plants (PAT plants), allowthe control both of the loading pressure and of the temperature in thepressure tank. Since the diffusion rate in polymers rises significantlyabove the glass transition temperature thereof, it is thus possible toachieve rapid pressure loading even of engineering plastics such as PBT.With modern PAT plants, it is possible to load particle foams with gasat pressures in the range from 0 to 14 bar and temperatures up to 200°C. In addition, the starting pellets may simultaneously also beautomatically coated with liquid, viscous or pulverulent functionalmaterials, for example for electrical conductivity or for coloureffects. By means of optimized pressure loading parameters, it waspossible, for example, to reduce the bulk density of expandedthermoplastics to such an extent and hence to produce mouldings that areeven 44% lighter than components foamed in a conventional manner. PATplants for use in accordance with the invention are available fromTeubert Maschinenbau GmbH, Blumberg, Germany as Teubert EPP Unimat orTeubert TVZ.

But the speed with which the polymer foam particles can be “filled” withair, nitrogen or carbon dioxide depends considerably on the temperatureconditions that exist. To date, industrially established pressureloading systems have worked solely at room temperature. More recentplants permit control both of the loading pressure and of thetemperature in the pressure tank. Since the diffusion rate inthermoplastics rises significantly above the glass transitiontemperature thereof, it is thus possible to achieve rapid pressureloading even of engineering plastics such as PBT.

By virtue of the combination of additive mould manufacturing andcompletely steam-free processing, modern methods in combination withPET- and preferably additionally talc-modified PBT are opening upcompletely new perspectives with regard to functionalization andlightweight construction. For instance, it is possible to manufacturemouldings with local reinforcements and from gradient and mixedmaterials in situ, i.e. in a process-integrated, straight-from-the-mouldand reprocessing-free manner. Surfaces can be configured virtually asdesired by virtue of textiles, films and structural elements, up to andincluding paper, introduced into the mould. In-mould coating of metal orplastic elements, even in unencased form, and of electronic or opticalcomponents is likewise readily possible.

Further application potential arises, for process-related reasons, inclosed structures. Sandwich structures provided with impermeable outerlayers on multiple sides can now be manufactured “in-process” in asteam-free manner with PET- and preferably additionally talc-modifiedPBT. This innovative approach to particle foam processing offersnumerous options and new applications, especially in lightweightconstruction through locally functionalized material use.

The subsequently stabilized polymer foam particles obtainable inaccordance with the invention from the expansion process, especiallyfrom the continuous infrared oven, can then be processed furtherdirectly, or else only after storage, in a further step to give productsor shaped bodies. For the in-mould foaming, a variothermallytemperature-controllable mould is used in accordance with the invention.

The invention also relates to products or shaped bodies based on theabove-described polymer foam particles, or those obtainable by the aboveprocess, by supplying them to a variothermally temperature-controllablemould. The invention therefore also relates to products or shaped bodiesthat are obtainable by prefoaming of polymer foam particles by the aboveprocess with energy input and supply thereof to a variothermallytemperature-controllable mould for the purpose of moulding.

The specimens obtained by steam-free foam moulding on the pilot scaleare formed with the aid of highly thermally dynamic moulds (heating andcooling rates of up to 30 K/second). In the range from room temperature(23+/−2° C.) up to about 190° C.—with more than 250° C. beingtechnically possible—cycle times of less than one minute are achieveddepending on the target wall thickness. In principle, sandwichstructures, as particular embodiments of particle foam mouldingsaccording to the invention, always consist of two high-strength andstiff outer layers bonded to a rigid core material of minimum weight byan adhesive boundary layer. The outer layers absorb tensile forces onthe top side and compressive forces on the bottom side that arise understress, while the core is responsible for the transmission of shearforces. As a result of the increase in the separation of the two outerlayers from one another, stiffness and strength are multiplied, whilethe weight of a sandwich structure according to the invention rises onlyslightly on account of the low density of the core material.

In the steam-free particle foam processing according to the invention bymeans of highly dynamic variothermal mould technology, highly dynamicvariothermal mould cavities are used. By virtue of high-precisionheating and cooling of the mould cavities, it is possible to heat thepolymer foam particles by means of radiative heat from the mould cavitywall and conduction of heat in such a way that they melt at the surfaceand hence are welded, but do not melt into the core. Depending on thetemperature control unit used and the temperature control medium,processing temperatures well above 160° C. are even possible, and infact even temperatures for processing of PET-blended PBT to be used inaccordance with the invention of well above 200° C. are achievable inaccordance with the invention.

Steam-free particle foam processing by means of highly dynamicvariothermal mould technology additionally permits the processing ofhydrolysis-sensitive materials/components as required for electroniccomponents/sensors, or the production of particle foam cores that are tobe completely encased by films or fibre composite outer layers.

By virtue of the inventive use of PBT in combination with PET andadditionally preferably in the presence of talc, it is now possible toopen up fields of use that have hitherto been closed to conventionalparticle foams. On account of the ever more compact design of enginesand the associated evolution of heat, according to the invention,PET-modified E-PBT (E for expanded) is a suitable candidate for enginespace insulation. It is now likewise possible to introduce E-PBT thathas been PET-modified in accordance with the invention, even at a veryearly stage of production, into chassis elements that then pass throughthe painting process in a composite, especially in cathodicelectrocoating baths and drying tunnels with relatively hightemperatures (30 minutes at up to about 200° C.).

Processes and moulds to be used for steam-free particle foam processingby means of highly dynamic variothermal mould technology for productionof large-volume or thick-wall particle foam components are described inDE 10 2018 007 301 A1, in EP 3 560 674 A1 and in EP 3 560 673 A1. Ameasure used here for binding of the particle foam material or of theparticle foam particles is steam-free exposure of the particle foammaterial or of the particle foam material particles to thermal energy(heat). The thermal energy may lead to bonding/fusion/sintering of atleast sections of the particle foam material or of the particle foammaterial particles. In principle, both conductive and convective modesof energy introduction and energy transfer are useful. The thermalenergy can be introduced into the particle foam material or the particlefoam material particles, for example, via energy transfer from at leastone temperature-controllable or temperature-controlled mould wallsection of a mould. In order to achieve uniform melting of the particlefoam material in the in-mould foaming process, the heat from thevariothermally temperature-controllable mould must penetrate into themiddle of the polymer foam moulding.

The invention preferably also relates to the use of polyethyleneterephthalate for broadening the processing window of polybutyleneterephthalate as matrix polymer in the production of polymer foamparticles by extending the melting range of polybutylene terephthalatefrom 225° C.+/−2° C. to the range from 223 to 255° C., wherein 25 to 320parts by mass of polyethylene terephthalate, 0.1 to 20 parts by mass oftalc and 0.01 to 20 parts by mass of tetrakis(2,4-di-tert-butylphenyl)4,4-biphenyldiphosphonite (Hostanox® P-EPQ) are used per 100 parts bymass of polybutylene terephthalate.

The use according to the invention preferably relates to the broadeningof the processing window in steam-free particle foam processing to giveparticle foam products or mouldings by means of highly dynamicvariothermal mould technology. More preferably, this use according tothe invention is effected in a variothermal mould with a flash face forpressurization.

“Variothermal” is composed of “vario” (Latin: be different, vary,fluctuate) and “thermal” (warm). The term “variothermal” is usedrelatively frequently in injection moulding in the sense of a “methodthat controls the temperature of moulds in a concerted manner over thecourse of the cycle”. The principle of highly dynamic variothermal mouldtechnology is a variothermal method of mould temperature control inwhich the mould cavity is preadjusted to such a temperature that thepolymer remains molten after injection, which achieves a precise imageof the surface fineness in the mould and a streak-free surface. Byvirtue of an optimized temperature control system with near-contourcavity surface temperature control, the variothermal process requiresonly insignificantly longer cooling times than the conventional steamoperated process. Further advantages are the absence of visible weldlines in the end product, and a considerable reduction in componentwarpage. This technology is already being used in injection mouldingprocesses. Advantages are a higher quality of the component surfaces,very good contour trueness, and the possibility of moulding of verysmall micro- and nanostructures. In this regard see: Development projectsupported under ref.: 32539/01 by the German Federal EnvironmentalFoundation, M. Feurer, A. Ungerer, “Die Entwicklung einerVariotherm-Technologie zur Halbierung des Energieverbrauchs in derEPP-Formteilherstellung” [The Development of a Variothermal Technologyfor Halving the Energy Consumption in EPP Moulding Production] fromApril 2017. The content of this reference is fully encompassed by thepresent application, with EPP standing for expanded polypropylene.

The inventive use serves for production of structural foam and/orinsulation foam, with structural foaming in one embodiment relating tosandwich structures. Structural foams or insulation foams according tothe invention are preferably used in high-performance lightweightconstruction. PBT-based products composed of expanded PBT particle foamwith typical densities in the range from 200 to 800 kg/m³ that areobtainable in accordance with the invention are extremely light.Specifically for that reason, they are notable for good specificmechanical properties, thermal insulatability and enormous lightweightconstruction potential.

Preferred fields of use for structural foams and/or insulation foams arein aerospace, in defence technology, in wind power rotor blades, inautomobile construction or in shipbuilding.

It will be understood that the specification and examples areillustrative but not limitative of the present invention and that otherembodiments within the spirit and scope of the invention will suggestthemselves to those skilled in the art.

EXAMPLES

Production of Polymer Foam Particles

The CO₂ loading of a PET-modified PBT pellet material according to theinvention, additionally containing talc and Hostanox® P-EPQ, and havinga grain diameter in the range from 0.5 to 2 mm and a length in the rangefrom 0.5 to 3 mm, was conducted in an autoclave at a pressure of 10 to70 bar over a period of 5 to 50 h. Subsequently, the CO₂-laden PBTpellets were guided through a continuous infrared oven (single-lane SLcontinuous infrared oven from Fox Velution GmbH) with a source power of90% (here: about 20 kW) at a temperature measured at the oven exit inthe range from 220 to 255° C. (merely reference band temperatures weremeasured optically—a wide variety of temperatures from 50° C. to 950° C.existed at different positions in the oven) at a speed of 500 to 800mm/s. Finally, the particles were stabilized at room temperature for 24hours.

The experiments in the context of the present invention additionallyshowed that, surprisingly, the use of PET in PBT reduced the growth rateof polymer foam cells that arise at the nucleation points. This resultsin polymer foam cells at more nucleation points. This in turn led topolymer foam particles having a more uniform cell structure of smallcells.

The inventive use of PET in PBT additionally increases melt viscosity.Particularly at low shear rates in the range from 50 to 200 Pa·s, asoccur in cell growth. With PET contents >25% on foaming in a continuousinfrared oven, the melt viscosity of the PET-modified PBT, relative tostandard PBT, rose from 109 to 112 Pa·s up to >200 Pa·s.

The rheological data in Tab. 1 show that the use of PET in PBT leads toa much higher melt viscosity in the low shear rate range, which isessential especially in the expansion of the cells and hence for cellgrowth.

The inventive use of PET in PBT, on the other hand, led to only a slightincrease in the density of the pellets before foaming from 1.319 g/cm³to 1.346 g/cm³, and is negligible with a difference of about 2%.

In-Mould Foaming

The polymer foam particles were moulded in an in-mould foaming processin a variothermally heatable mould with the temperature in the range of225-255° C. to give cubes as illustrative moulding having dimensions of25·25·10 mm. The heating rate of the mould was up to 8 K/s and the holdtime at temperature was 5-15 min. After the moulding, the mould wascooled down to room temperature at a cooling rate of up to 8 K/s, andthe moulding was parted from the mould and removed. The density of thecubes after 24 hours at room temperature was 392 kg/m³.

Surprisingly, the inventive use of PET in PBT-based polymer foamparticles, especially in combination with talc and very especiallypreferably additionally with Hostanox® P-EPQ, led to broadening of theprocess window in in-mould foaming from <4 K to <30 K when it wasconducted in a steam-free manner in a variothermally heatable mould at atemperature in the range of 225-255° C.

Feedstocks

Polybutylene terephthalate (PBT): Pocan® B 1300 from Lanxess DeutschlandGmbH;

Polyethylene terephthalate (PET): Lighter C88 from Equipolymers s.r.l.,Amsterdam, the Netherlands;

Talc: Mistron® R10 from Imerys Talc Group, Toulouse, France

Hostanox® P-EPQ, manufacturer: BASF SE, Ludwigshafen

TABLE 1 Unit Comp. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 PBT [% by 99.4 74.4 74.449.4 64.4 wt.] PET [% by 25 25 50 35 wt.] TALC [% by 0.5 0.5 0.5 0.5 0.5wt.] HOSTANOX ® P-EPQ [% by 0.1 0.1 0.1 0.1 0.1 wt.] Technology E/U*E/U* A/IR* E/U* A/IR* Bulk density of polymer [kg/m³] 173 276 218 16095-294 foam particles Moulded foam 231 236 236 230 236 temperature Min.moulded foam [° C.] 230 225 225 225 225 temperature Max. moulded foam [°C.] 232 255 255 255 257 temperature Moulded foam process kelvin <2 <30<30 <30 <32 window Foam particle cell size (mm) 0.2 0.55 0.1 0.5 0.05Rheological tests Moisture content by [%] 0.007 0.005 0.005 0.002 n.a.Karl Fischer (visco.) Melt viscosity 260°C [Pas] 111 149 149 244 285 ETA(50/s) Melt viscosity 260°C [Pas] 112 135 135 219 250 ETA (100/s) Meltviscosity 260°C [Pas] 109 138 138 215 248 ETA (200/s) Melt viscosity260^(o)C [Pas] 113 136 136 188 214 ETA (500/s) Melt viscosity 260^(o)C[Pas] 99 120 120 155 176 ETA (1000/s) Melt viscosity 260^(o)C [Pas] 92114 114 134 152 ETA (1500/s) Melt viscosity 260^(o)C [Pas] 62 71 71 8391 ETA (5000/s) *E/U = extrusion with blowing agent and underwaterpelletization **A/IR = autoclave gas loading and foaming in continuousinfrared oven

What is claimed is:
 1. A polymer foam particle comprising at least oneblowing agent selected from the group of air, nitrogen and carbondioxide, and 25 to 320 parts by mass of polyethylene terephthalate per100 parts by mass of polybutylene terephthalate.
 2. A polymer foamparticle according to claim 1, wherein such particle has a density inthe range of from 50 to 700 kg/m³.
 3. A polymer foam particle accordingto claim 1, wherein such particle has a density in the range of from 90to 400 kg/m³.
 4. A polymer foam particle according to claim 1, whereinsuch particle contains 0.1 to 20 parts by mass of talc.
 5. A polymerfoam particle according to claim 1, wherein such particle contains 0.1to 5 parts by mass of talc.
 6. A polymer foam particle according toclaim 4, wherein such particle contains per 100 parts by mass ofpolybutylene terephthalate, in addition to talc, 0.1 to 20 parts by massof at least one further additive other than talc.
 7. A polymer foamparticle according to claim 4, wherein such particle contains per 100parts by mass of polybutylene terephthalate, in addition to talc, 0.1 to5 parts by mass of at least one further additive other than talc.
 8. Apolymer foam particle according to claim 6, wherein the at least onefurther additive is selected from the group of UV stabilizers, thermalstabilizers, lubricants, demoulding agents, fillers, reinforcers,nucleating agents, laser absorbers, di- or polyfunctional branching orchain-extending additives, hydrolysis stabilizers, antistats,emulsifiers, plasticizers, processing auxiliaries, flow auxiliaries,elastomer modifiers and colourants.
 9. A polymer foam particle accordingto claim 6, wherein the at least one further additive istetrakis(2,4-di-tert-butylphenyl) 4,4-biphenyldiphosphonite.
 10. Aprocess for producing polymer foam particles, comprising (a) introducingpowders or pellets of a polymer matrix into an extruder with exclusionof crosslinking agents and/or chain-extending agents and plastifying andhomogenizing the powders or pellets, (b) adding and dispersing into theplastified polymer matrix a blowing agent selected from the group ofair, nitrogen and carbon dioxide, (c) discharging the plastified polymermatrix with the added blowing agent through an extruder die, (d)pelletizing downstream of the extruder die the extruded polymer matrixstrand with the added blowing agent to form expandable or at leastpartly expanded polymer foam particles, and (e) expanding the polymerfoam particles, wherein the polymer matrix contains 25 to 320 parts bymass of polyethylene terephthalate per 100 parts by mass of polybutyleneterephthalate.
 11. A process according to claim 10, wherein processsteps (c) and (d) are performed with or in a cooling fluid.
 12. Aprocess according to claim 10, wherein process step (e) is effected in acontinuous infrared oven.
 13. A process according to claim 10, whereinthe polymer foam particles have a density in the range from 50 to 700kg/m³.
 14. A process according to claim 10, wherein the polymer foamparticles have a density in the range from 90 to 400 kg/m³.
 15. Aprocess according to claim 13, wherein the polymer matrix contains 0.1to 20 parts by mass of talc.
 16. A process according to claim 13,wherein the polymer matrix contains 0.1 to 5 parts by mass of talc. 17.A process according to claim 15, wherein the polymer matrix additionallycontains 0.1 to 20 parts by mass of at least one additive other thantalc.
 18. A process according to claim 15, wherein the polymer matrixadditionally contains 0.1 to 5 parts by mass of at least one additiveother than talc.
 19. A process according to claim 17, wherein the leastone additive other than talc is selected from the group of UVstabilizers, thermal stabilizers, lubricants, demoulding agents,fillers, reinforcers, nucleating agents, laser absorbers, di- orpolyfunctional branching or chain-extending additives, hydrolysisstabilizers, antistats, emulsifiers, plasticizers, processingauxiliaries, flow auxiliaries, elastomer modifiers and colourants.
 20. Aprocess according to claim 17, wherein the at least one additive otherthan talc is tetrakis(2,4-di-tert-butylphenyl)4,4-biphenyldiphosphonite.
 21. A method for broadening the temperatureprocessing window of polybutylene terephthalate (PBT) in the form ofmatrix polymer-containing expandable or at least partly expanded polymerfoam particles in in-mould foaming, comprising forming a polymer matrixbased on a blend comprising polyethylene terephthalate and polybutyleneterephthalate for preparing the polymer foam particles, wherein thepolymer matrix contains 25 to 320 parts by mass of polyethyleneterephthalate per 100 parts by mass of polybutylene terephthalate. 22.The method according to claim 21, wherein the temperature processingwindow is for in-mould foaming by means of steam-free particle foamprocessing to give particle foam mouldings in a variothermally heatablemould.
 23. The method according to claim 21, wherein the temperatureprocessing window is for in-mould foaming for production of structuralfoam or insulation foam.
 24. The method according to claim 23, whereinthe structural foam is of a sandwich-type structure.
 25. A method forincreasing the melt viscosity of polybutylene terephthalate as a matrixpolymer for expandable or at least partly expanded polymer foamparticles, comprising processing polybutylene terephthalate withpolyethylene terephthalate in a polymer matrix for preparing expandableor at least partly expanded polymer foam particles, wherein the polymermatrix contains 25 to 320 parts by mass of polyethylene terephthalateper 100 parts by mass of polybutylene terephthalate.
 26. A particle foammoulding produced by prefoaming the polymer foam particles according toclaim 1 and moulding the prefoamed particles in a variothermallytemperature-controllable mould.